Temperature sensor employing married diode junction means

ABSTRACT

An improved system employing a plurality of economical, linear and interchangeable temperature sensors, characterized by (1) diode junction temperature sensors that include a plurality of serially connected diode junctions that are preselected to have a predetermined standard operating curve, at a constant current within the range of - 100* F. to + 350* F.; and (2) power supply means and regulator means for maintaining a substantially constant current flowing through the diode junction temperature sensor. Also disclosed are specific embodiments including: (1) temperature sensors connected with an electrical common and employing a single readout lead carrying a signal that is relatively insensitive to the length of the lead, and (2) multiplexing equipment for monitoring a plurality of such readout leads.

United States Patent I191v Stout et al.

1 5] Feb. 12, 1974 1 1 TEMPERATURE SENSOR EMPLOYING MARRIED DIoDEJUNCTION MEANs [75] Inventors: Beauiord F. Stout, Grandview;

George W. Hann, Fort Worth, both of Tex. [73] Assignee: Kodata, In c.,FortWorth, Tex. [22 Filed: Nov. 8,1971 I [21] Appl. No.: 196,269

[52] US. Cl 73/342, 73/362 SC, 317/235 Q [51] Int. Cl. G0lk 7/24, H0111/22 [58] Field of Search 73/342, 362 AR, 362 SC;

[56] References Cited UNITED STATES PATENTS" 3,330,158 7/1967 Simonyanet al. 73/362 SC 2,098,650 11/1937 Stein 73/362 AR 3,575,053 4/1971Telinde 73/362 AR 3,211,000 10/1965 Childs 73/342 3,271,660 9/1966Hilbiber 307/310 X 3,440,883 4/1969 Lightner 73/362 SC PrimaryExaminer--Richard C. Queisser Assistant Examiner-Frderick ShoonAttorney, Agent, or Firm-Wofford, Felsman & Fails [57] ABSTRACT Animproved system employing a plurality of economical, linear andinterchangeable temperature sensors, characterized by (1) diode junctiontemperature sensors that include a plurality of serially connected 7diode junctions that are preselected to have a predetermined standardoperating curve, at a constant current within the range of 100 F. to+350 F.; and (2) power supply means and regulator means for maintaininga substantially constant current flowing through the diode junctiontemperature sensor. Also disclosed are specific embodiments including:(1)

v temperature sensors connected with an electrical common and employinga single readout lead carrying a signal that is relatively insensitiveto the length of the lead, and (2) multiplexing equipment for monitoringa plurality of such readout leads.

5 Claims, 6 Drawing Figures REG. MNS. AND TEMP. SENSOR 57 TEMP(F).QMENTEDFEB 12 I874 3.791217 sum 1 ur 2 J ZCZ REG. MNS. AND

TEMP. SENSOR 3'7 on; o la 1 42 0 axee LL J a cane 910 o TEMP (F)BACKGROUND OF THE INVENTION 1. Field of the Invention This inventionrelates to solid state temperature measuring devices. More particularly,it relates to an improved system employing a plurality of temperaturesensors wherein economy, linearity and interchangeability of thetemperature sensors is'a desirable feature.

2. Description of the Prior Art 7 The art of thermometry has seen thedevelopment of widely varying approaches ranging from conventional fluidthermometers through solid state temperature measuring devices. Thelatter have included reverse biased and forward biased semiconductorjunctions. Suchsolid state temperature measuring devices are typified byU.S. Pat. Nos. 3,330,158; 3,421,375; and 3,430,077. As is pointed out inone or more of these patents, it has been generally recognizedheretofore that simple diode thermometry was economically infeasible andimpractical; particularly, where the system employed a large number ofthe thermometers and interchangeability was required. This was dueprimarily to the fact that only about one percent of the economicalcommercially available diodes had the necessary same performance curve.The other diodes departed too much from any one performance curveselected as a standard. A variety of systems were adverted to tocompensate for this lack of standard performance. Insofar as we areaware, however, the prior art has not succeeded in providing.economical, linear diode thermometers that could be employed in a systemwith other diode thermometers and provide the requisiteinterchangeability without introducing significant errors into thesystem, or without requiring a recalibration of a particular one ofindividual auxiliary components of the system, or the like.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an isometric view of atemperature measuring device of one embodiment of this invention.

FIG. 2 is a schematic diagram of one embodiment of this inventionemploying the temperature measuring device of FIG. 1. v

FIG. 3 is a schematic diagram of one temperature measuring deviceconnected with monitoring equipment in accordance with an embodiment ofthis invention. a 1

FIG. 4 is a schematic diagram of a typical gate which may be employed inthe embodiment of FIG. 3 in order to employ a plurality of temperaturesensors in a single monitoring system.

FIG. 5 is a graph of operating, or performance, curves such as areemployed in effecting the diode thermometer by combining diode junctionsto have the desired operating characteristics and the requisite economy,linearity and interchangeability.

FIG. 6 is an electrical schematic diagram of a system incorporatingmultiplexing equipment and a plurality of temperature sensors inaccordance with an embodiment of this invention.

DESCRIPTION OF PREFERRED EMBODIMENTS It is an object of this inventionto provide a system employing a plurality of diode thermometers thatobviate the disadvantages of the prior art. Specifically, it is anobject of this invention to provide a system employing a plurality oftemperature sensors that are economical, linear and interchangeable suchthat any one may be replaced without requiring a recalibration, withoutrequiring supplemental auxiliary equipment, and without introducingsignificant error into the temperature measured by the system.

Other objects of this invention will become apparent from the followingdescriptive matter when taken in conjunction with the drawings.-

The invention comprises an improvement in a system employing a pluralityof temperature sensors wherein economy, linearity and interchangeabilitythereof is a desirable feature. The improvement includes using diodejunction temperature sensors for measuring the temperature, and powersupply means and regulator means for maintaining a constant currentflowing through the diode junction temperature sensor. The diodejunction temperature sensors have a standard performance curve defininga predetermined voltage drop across the sensor at a predeterminedtemperature and a constant current flow and a voltage drop that variessubstantially linearly with temperature at the constant current withinthe range of at least -50 F to +250 F. for the desiredinterchangeability. The diode junction temperature sensor includes aplurality of diode junctions that are pre-selected to have a summationof their respective departures from the predetermined standardperformance curve be substantially zero and that are serially connectedsuch that the diode junction temperature sensor has the standardperformance characteristics. The power supply means and regulator meansare-serially connected with the diode junction temperature sensor in theforward biased direction.

*Referring to the figures, FIG. 1 illustrates a typical physical form ofa commercially available temperature measuring device 11 and its threeleads 12-14. The

temperature measuring device 11 may include only the diode junctionsensor, or it may include, as illustrated in FIGS. 1 and 3, both thediode junction temperature sensor 15 and the regulator means 17. As hasbeen recognized in the art and indicated hereinbefore, economicallyfeasible, commercially available diodes do not have the same performancecurves for a variety of reasons; such as, doping levels, transientimpurities, different temperature levels during fabrication and thelike. Random pairing has been employed hereinbefore to raise the signallevel of the plurality of serially connected diodes. Such random pairinghas frequently only worsened the lack of interchangeability, since thedepartures from a standard performance curve by each of the diodes werefrequently additive. Consequently, diode therrnometry has beenrestricted to scientific uses or in applications where only a singlethermometer and readout equipment was required; and it has not achievedthe widespread use possible where multiplexing equipment was employed ina system for monitoring a plurality of temepratures at widely spacedlocations; such as illustrated by the different locations 19, 21 and 23,FIG. 2. As illustrated in FIG. 2, the locations are disposed in anapartment complex 25. The loca- We have found, however, that economical,linear, and interchangeable diode junction temperature sensors are madepossible by the following process. A batch of commercially availablediodes are pre-tested, separated, and catalogued according to theirrespective performance curves, as illustrated in FIG. 5. The diodes arecombined in a predetermined plurality such that the sum of theirdepartures from an ordinary performance curve is zero. Any desiredplurality may be employed, depending upon the magnitude signal desired.As many as 50 or more may be combined for a signal level that does notrequire amplification. Ordinarily, 2, 3 or 4 diode junctions will beadequate. For example, as illustrated in FIG. 5, a first diode of a pairof diodes may have a performance curve 27, defining a first voltage drop(A v) across the diode at a predetermined temperature and a constantcurrent flow therethrough. As illustrated in FIG. 5, the voltage drop inmillivolts direct current (mv DC) is plotted as a function of thetemperature (temp) in F. Thus, the first diode will be placed in a bin,or receptacle, for diodes having a first voltage drop at thepredetermined temperature, illustrated as a difference in voltage drops(A V1) between the performance curve 27 and a standard performance curve29. In the case of the first diode, the difference will be a negativeAVl, having a predetermined absolute value. In making up the diodejunction temperature sensor, it is then paired with a second diodehaving a performance curve 31, such that at the predeter minedtemperature -the difference between the performance curves, A V2, hasthe same absolute value as A V1 but is a positive difference. Thus, thesummation of their respective departures from the predetermined standardperformance curve 29, (A Vl A V2), is substantially zero.

By the described process, all of the diode junction temperature sensors;such as diode junction temperature sensor 15 employing two diodejunctions; will be economical, since substantially all of the diodeswill be employed instead of the very low percentage that would otherwisehave the same performance characteristics. Also, the diode junctiontemperature sensors will have the desired linearity, since such diodejunction temperature sensors are linear and have voltage drops that areinversely proportional to the temperature over the range of 50 F to +250F; and are operably linear and proportional over the range of l F to+350 F.

The temperature measuring device 11 has a low mass such that it issensitive to temperature change. It may be prepared in three differenttypes of pots, or finished packages. For example, it may be prepared asan ambient air sensor for mounting under a ventilated cover orthermostat housing, as a duct sensor for mounting directly in an airconditioning duct, or as an immersion sensor for mounting in a thermalwell or the like. If desired, it can be prepared for immersion directlyin a fluid whose temeprature is to be measured, although the latter isnormally not advisable, since removal from such an installation wouldnecessitate stopping the flow of the fluid and thermal wells areordinarily desirable. As illustrated in FIG. I, the serially connected,or married, diodes forming the diode junction temperature sensor 15, andthe regulator means 17 may be emplaced in a thin-walled, heat conductivecontainer such as a container of aluminum, and potted in epoxy resin.

Any of the known power supply means and regulator means may be employedfor maintaining the requisite substantially constant current flowingthrough the diode junction temperature sensor. As illustrated in FIG. 3,the power supply means may comprise any direct current power sourceconnected with terminal 37, which is connected with lead 12. Preferably,however, a constant voltage power supply is employed. For example, wehave found it advantageous to employ a single power supply thatregulates the voltage within 10.01 percent when regulating at 24 voltsDC. It is noteworthy, however, that as much as 0.5 volts deviation inthe voltage of the power supply will produce errors of less than onedegree Fahrenheit in the measured temperature. A typical constantvoltage power supply is illustrated in FIG. 6 and described hereinafterwith respect to the multiplexing equipment. In FIG. 2 the plurality ofterminals 37 may be connected in parallel and with a single regulatedvoltage power supply such as constant voltage power supply 39, FIG. 6.

Illustrative of regulator means for controlling constant current are thewell known elaborate constant current regulators. As described in ourcopending application Ser. No. 855,982, entitled Measuring BoreholeTemperatures Employing Diode Junction Means, a field effect transistormay be employed to maintain the current constant. We have found,however, that with a constant voltage power supply, we can effect acurrent flow that is sufficiently constant for most surface temperaturemonitoring installations with a relatively high resistance resistor,such as illustrated in FIG. 3. The surface temperature monitoringinstallations will not ordinarily be subjected to the wide variation intemperature that may be encountered in boreholes, so the substantiallyconstant current effected by the relatively high resistance, illustratedas regulator means 17 is adequate. Preferably, however, the resistor hasa zero temperature coefficient such that its resistance does not changeeven if the temperature to which it is subjected should change, asbetween daylight and night time hours. Such resistors having zerotemperature coefficient are known in the art, and are typified by theCorning glass resistors, which are also rugged and appropriate fortemperature monitoring installations. Moreover, these zero temperaturecoefficient resistors are amenable to being potted with the diodes in atemperature measuring device 11, as described hereinbefore. They aresufficiently accurate and standard in value of resistance thatinterchangeability of the temperature measuring devices made with thempresents no problem. The magnitude of the resistance of the resistors ischosen to effect the desired flow of current through the diode junctiontemperature sensors at the voltage of the power source. We have found itdesirable to employ temperature measuring devices that require less thanone milliamp of current flow, or current drain. Thus, current may beflowed continuously through the diode junction temperature sensor and avoltage which is a function of the temperature being measured maintainedon its readout line 13 for rapid scanning, or monitoring, by themultiplexing equipment. Specifically, we have found a current of aboutmicroamperes per diode junction temperature sensor may be maintainedcontinuously without appreciable current drain and without heating thediode junction temperature sensor. In this way, a power supply that willsupply one-half an ampere of current will excite up to 5,000

sensors simutaneously.

Referring further to FIG. 3 for a hook-up of a single temperaturemeasuring device 11, the readout lead 13 is connected with an inputterminal of operational amplifier 41. Suitable operational amplifiersare commercially available; for example, the Philbrick Nexus No. 1009for matching inpedance. As illustrated, the lead 13 is seriallyconnected with the operational amplifier 41 via resistor 43. If desired,as for use in multiplexing equipment, it may include a gate means 45. Asillustrated in FIG. 4, the gate means 45 may comprise a field effecttransistor (FET) 47 having its gate 49 connected with the multiplexingequipment. Upon the occurrence of an appropriate signal on gate 49, theBET 47 will effect the desired interconnection between the operationalamplifier at the central location illustrated by panel 51, FIG. 2, andthe temperature measuring device 11 at the site where the temperature isto be measured. The operation of the gate means will become clearer withthe descriptive matter regarding FIG. 6 hereinafter. The operationalamplifier 41 may be a field effect operational amplifier (FET OP AMP).Such operational amplifiers ordinarily have a very high impedance suchas 10,000,000 ohms so that they can sample the voltage on the readoutlead 13 without appreciable current flow. Thus, the temperature that ismeasured becomes relatively insensitive to the length of readout lead13, because of the lack of appreciable current flow. Consequently,temperature can be measured at widely varying physical locations; andmonitored and controlled at a single control point typified by panel 51,FIG. 2.

The operational amplifier 41 may also be used to suppress the basevoltage of the temperature sensor at a predetermined temperature andinvert the sensor output to effect a positive temperature coefficient.As illustrated in FIG. 3, the operational amplifier 41 is connected viasuitable wiper means 53 with a dividing resistor 55. The dividingresistor 55 is serially connected with terminals 57 and 59 on which areimposed suitable voltages; for example, a positive volts on one terminaland a negative 15 volts on the other. In this way, the wiper means 53may be positioned to buck out the base voltage. To illustrate, if arange of 0-300 millivolts is desired as an output from the operationalamplifier 41 in response to a temperature range of from 0-300 F, thewiper means 53 may be positioned on the dividing resistor 55 to buck outthe base voltage of about 3.218

volts DC for a six diode junction temperature sensor 15 at, 100 F. Theoperational amplifier, being an inverting amplifier, will thereafterconvert, for example, decreasing voltages on readout lead 13 effected byincreasing temperatures inversely into an output in which the increasein output is equivalent to the increase in temperature sensed by thetemperature sensor 15. The opposite is effected in response todecreasing temperatures.

In operation, the diode junction temperature sensor 15 is seriallyconnected with electrical common, indicated by the ground symbol, withthe regulator means 17, and with the power supply means connected withamplifier 41. The operational amplifier 41 produces an output signal,such as a voltage on conductor 61. The output signal may be employed tooperate a temperature indicator such as a dial indicating thetemperature, or one or more lights'to indicate that the temperature ishigh or low. On the other hand, the output signal on conductor 61 may befed as an input signal to a controller which operates about apredetermined temperature or within a predetermined temperature range.For example, a controller may turn on an air conditioner if thetemperature goes above a predetermined maximum, or it may turn on aheater if the temperature goes below a predetermined minimum. Theoperation of temperature indicators or controllers when a predeterminedoutput signal is fed to them is well known; is not being claimed, perse, herein; and need not be further described in more detail herein.

FIG. 6 illustrates an interconnection of multiplexing apparatus at acentral station, typified by panel 51 in FIG. 2, and a plurality oftemperature measuring devices 11, including the remote regulator means(REG. MNS.) and temperature (TEMP.) sensor, at the position at which thetemperature is to be measured. Therein, a constant voltage power supply39 is provided for supplying power at different voltage levels inaccordance with the demands of the logic circuit being employed in themultiplexing equipment. As illustrated, the constant voltage powersupply employs integrated regulators (REG) 65 and 67 that provideadditive voltage outputs. For example, they provide 5 volt outputs suchthat the voltage V1 of 5 volts is supplied on the terminal 69 and thevoltage V2 of 10 volts is supplied on the terminal 71. The constantvoltage power supply 39 also provides a highly regulated voltage V3 forsupplying power to the temperature measuring devices 11. The voltage V3is supplied to terminal 73 and may be, for example, 24 volts. Thevoltage output on terminal V3 is highly regulated to a 0.01 percent, asindicated hereinbefore, and is conducted to the respective temperaturemeasuring devices 11, indicated by the voltage V3 on lead 12, FIG. 6.The regulation of voltage V3 is effected by a field effect transistor 75and serially connected Zener diodes 77, in the well known manner.Similarly, appropriate other voltages maybe regulated and tapped off;such as, the regulated voltage V4 maintained on the terminal 79. As canbe seen, Zenen diode 81, the capacitor 83 and resistor 85, inconjunction with diode 87 cooperate to provide the desired regulatedvoltage V4. The voltage V4 may be, for example, -l5 volts for theoperational amplifier 41. In like manner, a master voltage V5 may beprovided on terminal 89. The appropriate voltage outputs are provided byconnection with the secondary 91 of the transformer 93. The primary 95of the transformer may be connected with a conventional l 10 voltalternating current (AC) power source. The respective terminals carryingthe respective voltages are suitable connected with like-markedterminals in FIG. 6. The interconnecting conductors are omitted forsimplicity of illustration and clarity.

The constant voltage power supply 39 is also serially connected with thetrigger means 97 via conductor 99, diode 101 and resistor 103. Thetrigger means 97 includes a Schmitt trigger for pulse shaping. Theoutput terminal of the Schmitt trigger circuit is connected viaconductor 105 with the rate clock. The rate clock comprises a firstdividing circuit 107. For example, the first dividing circuit maydecrease the number of shaped pulses from the Schmitt trigger such thatevery third pulse is conducted therethrough. As illustrated, the rateclock also includes a second dividing circuit 109 which is connected viaconductor 111 with the first dividing circuit 107. For example, thesecond dividing circuit may conduct therethrough every tenth pulse onthe output from the first dividing circuit 107. Under such an example asdescribed, a 60 Hertz output from the Schmitt trigger will emerge as a 2Hertz output from the second dividing circuit 109. The dividing circuitsare also connected with the voltage source Vcc and with electricalcommon, or ground, as illustrated.

The output terminal of the second dividing circuit 109 is connencted viaconductor 113 with the shift register. Any of the conventional shiftregisters may be employed. For example, it may be a mechanicallyoperated stepping switch. Preferably, for high speed scanning, the shiftregister comprises a solid state shift register such as the SigneticsN8202N. As illustrated, the shift register includes a register, orcounting means 115, and conventional return and operational accessories;such as, logic elements, or NAND gates, 116-119 that are conventionallyemployed in shift registers, and the delay means 121. The delay means121 provides a 0.25 microsecond delay and is needed for proper operationof the shift register. As illustrated, the delay means 121 comprisesserially connected hex inverters 123 and 125, and resistor 127 that arealso serially connected to the output from logic element 119 and to oneinput terminal of the logic element 118. The juncture of resistor 127and hex inverter 125 is connected with ground via capacitor 129.Basically, the shift register operates in the fashion of a conventionalring counter in stepping the respective output signals from the secondclock unit 109 onto the gate means 45, FIG. 4, that will interconnectthe respective temperature measuring devices 11 with the amplifier 41.When the last temperature measuring device 11 has been monitored, theshift register effects a return of the first temperature measuringdevice 11 to repeat the cycle. The scanning rate may be at any desiredrate up to 1,000,000 times per second. Ordinarily, a scanning ratewithin the range of between a few times per second or less to -a fewthousands of times per second will be adequate. As indicated, theregister 115 is also serially connected with the voltage source Vcc andwith the electrical common, or ground.

As illustrated in FIG. 6, the respective outputs from the shift registerare connected to respective input terminals of elements in a translatormeans 131 for altering the logic output level. For example, the logicoutput from the shift register may be 5 volts. The translator means 131alters the 5 volts to 0 volts which is supplied to the gate means 45;and, specifically to gate 49, FIG. 4, of the field effect transistor 47.The zero voltage on gate 49 allows FET 47 to conduct. For example, therespective elements inside the translator means 131 may compriseconventional hex inverters (INV) 133. Thus, the respective hex inverters133 actually serve as drivers to drive the field effect transistors intoa conducting or nonconducting state in order to effect the scanning, orinterconnection, of the respective diode junction temperature sensorswith the respective monitoring means; such as, comprising operationalamplifier 41. If desired, compatible logic levels can be employed toobviate the necessity for the translator means 131.

The respective output terminals of the translator means 131 areconnected with respective input terminals on the gate means 45, asillustrated in FIGS. 4 and 6. The use of a plurality of field effecttransistors as gate means 45 is well known. For example, we have foundthat the Siliconix, DG172BK provides satisfactory gating for connectingthe respective temperature measuring devices 11 with the operationalamplifier 41 in response to a signal from translator means 131. Theoutput terminal 137 of the gate means 45 is connected with the inputterminal 139 of the operational amplifier 41 via conductor 141. Tehother input terminal of the operational amplifier 41 is connected viawiper means 53 with the resistor 55 for effecting the desired balancingof the operational amplifier, or suppression of the base voltage of thetemperature measuring device at a predetermined temperature, asdescribed hereinbefore. The operational amplifier 41 is also connectedwith the voltages V2 and V4. The resistor 55 is serially connected witha temperature compensated, regulated reference voltage source 143, suchthat any desired temperature threshold may be employed by biasing out apredetermined base voltage on the temperature measuring devices 11. Asillustrated, the reference voltage source 143 comprises the field effecttransistor 145 and resistor 147 serially connected with the voltagesource V5; with the conventional Zener diode 149 connected withelectrical common, or ground, for further fine voltage regulation.

As described with respect to FIG. 4, the output signal from operationalamplifier (OP AMP) 41 is impressed on conductor 61 for any desired use;such as, to energize a light indicating when the temperature is offcontrol, to actuate a controller, or to provide a visual indication oftemperature. As illustrated in FIG. 6, the conductor 61 is connected viaserially connected resistors 151 and 153 and inverting amplifier 155with the base of transistor 157. The transistor 157 is seriallyconnected to the juncture of the light emitting diodes (LED) 159 andresistor 161 and to electrical common. The juncture of the respectivelight emitting diodes 159 and resistor 161 is thus driven to ground bythe normally conductive transistor 157. The presence of a signal onconductor 61, however, turns off transistor 157 and provides the voltageVcc as power for the light emitting diodes 159. The light emittingdiodes 159 are connected, via their respective resistors 163 with thejuncture of the hex inverters 133' and the gate means 45 such that whenthe output of a hex inverter is driven to zero by a positive outputpulse on the shift register, an effective ground is also supplied to alight emitting diode and it will become energized. Diode clips anynegative signal from operational amplifier 41 on conductor 61 andprevents a negative signal on the hex inverters 133. The signal onconductor 61 also may be employed directly to operate a control device;or a control device may be optically coupled to the respective lightemitting diodes 159. There are a plurality of light emitting diodes 159,one for each temperature measuring device 11 and each is connected backto its respective interconnection between its hex inverter 133 and itsgate means 45.

The light emitting diodes 159 are thus connected such that they becomeenergized by, for example, a temperature drop of a small temperaturedifferential. For example, breadboard models have been so sensitive thatmerely moving the hand away from the temperature indicating device 11would cause a light emitting diode 159 to become energized. Controlwithin F is routine. While the illustrated connection will cause thelight emitting diode to become energized on a temperature drop of about0.5" F from the control' point; the opposite interconnection,illustrated by dashed lines 169 and 171, may be employed to cause thelight emitting diode to become energized on a temperature rise of thesame magnitude. Thus, it can be seen that two operational amplifiers maybe employed with their respective outputs connected directly tocontrollers; such as, for controlling either heaters or airconditioners, as the case may be.

In operation, the primary 95 of transformer 93 of the constant voltagepower source 39 is connected with a conventional source of power and thevarious voltages Vl-VS are supplied throughout the multiplex andtemperature measuring system. The trigger means 97 is started and theshaped pulse output from the Schmitt trigger operates the rate clock.The rate clock emits pulses which effect operation of the shiftregister. For example, the output from a first logic unit (LOG) 152 ofthe shift register is sent to the first hex inverter 133 in thetranslator means 131 and thence to the gate means 45. Accordingly, afirst temperature measuring device (not shown), comprising a regulatormeans and temperature sensor, is connected as by conductor 154 (showndiscontinuous) with the operational amplifier 41. As indicatedhereinbefore, the interconnection is made without appreciable currentflow such that the length of the conductor 154, which is the same as thereadout lead 13, is relatively immaterial. If the temeprature measuredat the first temperature measuring device 1 l is within control range,nothing happens. The shift register shifts at the next pulse from therate clock to connect, via hex inverter 133a, the second temperaturemeasuring device (not shown) via conductor 156. Effective ground issupplied simultaneously via resistor 163a to' light emitting diode 1590,just as it was to light emitting diode 159 as the first temperaturemeasuring devicewas monitored. Suppose that the second temperature wasoff its control point; for example, the temperature was too low.Accordingly, the operational amplifier 41 will effect an output signalon line 61 which will be suitably inverted by the inverting amplifier155 and turn 'off transistor 157, simultaneously supplying power to thelight emitting diode 159a. Accordingly, light emitting diode 159a willbe energized to indicate that the temperature is off control. .If acontroller is connected to the light emitting diode, as by anelectrooptic system, it will turn on a heater to supply heat to thatlocation.

The scanning of the temperatures and operation of respective controls(not shown) is continued through all of the temperature measuringdevices 11. Suitable controls are activated .to bring the respectivetemperatures within controlled limits. Thereafter, the logic elementseffect a return of the shift register to the first temperature measuringdevice and the cycle is repeated. A large number of temperaturemeasuring devices 11 may be emplaced throughout a large plant, or asillustrated in FIG. 2, an apartment complex; and the temperatures attheir respective locations monitored and controlled. With theillustrated solid state multiplexing equipment the temperature measuringdevices may be scanned as rapidly as needed to ensure continuity ofcontrol. Moreover, very little current is required to supply as many as3,0005,000 temperature measuring devices in a given industrial location.Since the cumulative parallel-connected impedance may be lowered to anappreciable degree with many; for example, more than 100; temperaturemeasuring devices connected in parallel, a plurality of banks; with eachbank having its own operational amplifier, or monitoring and controlequipment; may be employed.

From the foregoing descriptive matter and the drawings, it can be seenthat this invention provides temperature measuring devices thateliminate expensive thermocouple wire and cold junction compensationcommon in the prior art; and makes linearization of the readout deviceunnecessary, since each temperature measuring device has a high outputlevel (typically 3.218 volts DC at 100 F) and has a linear change(typically about 7.23 millivolts per degree Fahrenheit) that isinversely proportional to temperature. Because there is relativelylittle current flow through the readout leads connecting the temperaturemeasuring devices with the power supply and the multiplex equipment, orreadout device, and because the signal level is high, no shielding isrequired on the readout leads. The leads preferably arazz gauge copperwire or larger.

The temperature measuring devices may be employed in simple or complextemperature monitoring installations, but this invention has itsprincipal advantage wherein a plurality of temperature sensors areemployed with a single set of multiplexing equipment such thatinterchangeability and linearity are effected without the use of anyauxiliary equipment. Moreover, as indicated, the sensors may be locatedseveral thousand feet away from the readout device, since the leadlength effect is less than 0.2 F per 1,000 feet of distance. Also, onlysingle wire switching is necessary when the temperature measuringdevices are connected with an electrical common with which themultiplexing equipment is also connected, thereby reducing multiplexingcosts. Furthermore, as indicated hereinbefore, the temperature measuringdevices; and particularly the diode junction temperature sensors; arecompletely interchangeable without the need for recalibration. Thus, anyone may be replaced with another of the same number of diode junctionsand not introduce significant error into the system. With these specificadvantages in mind, it can be seen that the invention provides theobjects delineated hereinbefore and specifically .provides aneconomical, linear, interchangeable temperature measuring device,including a diode junction temperature sensor comprising a plurality ofmarried diode junctions.

Although the invention has been described with a certain degree ofparticularlty, it is understood that the present disclosure has beenmade only by way of example and that numerous changes in the details ofconstruction and the combination and arrangement of parts may beresorted to without departing from the spirit and the scope of theinvention.

What is claimed is:

1. In a system employing a plurality of temperature sensors, theimprovement comprising:

a. a diode junction temperature sensor for measuring the temperature;said diode junction temperature sensor including a plurality of diodejunctions that are serially connected, each diode junction having anoperating curve that is difierent from a predetermined standardoperating curve; said diode junctions being pre-selected to have asummation of their respective departures from said predeterminedstandard operating curve substantially zero whereby said diode junctiontemperature sensor has a predetermined voltage drop at a predeterminedtemperature and a predetermined constant current flow therethrough andhas a substantially linearly varying voltage drop at said predeterminedconstant current within the range of 50 F. to +250 F. for the requisiteeconomy, linearity and interchangeability; b.'power supply means andregulator means for maintaining a substantially constant current flowingthrough said diode junction temperature sensor; said power supply meansand said regulator means being serially connected with said diodejunction temperature sensor in the forward biased direction; said diodejunction temperature sensor being serially connected to electricalcommon; and a readout lead connected with the juncture of said diodejunction temperature sensor and said regulator means such that voltageis measured with respect to said electrical common to form a signal thatis a function of the sensed temperature; said voltage being sensed withno substantial current flow on the readout lead so as to be insensitiveto.

the length of said readout lead; said readout lead being adapted to beconnected into readout means for monitoring the sensed temperature suchthat any temperature sensor in said system may be replaced withoutrecalibration and without introducing significant error into the system.

2. The system of claim I wherein said regulator means and said diodejunction temperature sensor are incorporated into a single temperaturemeasuring device having a first lead that is connected with said powersupply means, a second lead that is connected with said electricalcommon and said readout lead is connected with a readout means formonitoring the sensed temperature.

3. The system of claim 1 wherein said system includes multiplexingapparatus that is connected with a plurality of said readout leads ofsaid respective diode junction temperature sensors, wherein each saidregulator means and diode junction temperature sensor pass asubstantially constant current that is sufficiently low such that is maybe passed continuously without appreciable power consumption and withoutheating said diode junction temperature sensor, and the constant currentfrom said power supply means and said regulator means is continuouslypassed through said diode junction means whereby said multiplexingapparatus may scan rapidly through the readout leads of said diodejunction temperature sensors for monitoring temperatures at a pluralityof widely scattered locations without appreciable instrument lag timebeing elapsed between respective monitorings.

4. The system of claim 1 wherein said constant current is less than 1millampere.

5. The system of claim 1 wherein said constant current is aboutmicroamperes.

1. In a system employing a plurality of temperature sensors, theimprovement comprising: a. a diode junction temperature sensor formeasuring the temperature; said diode junction temperature sensorincluding a plurality of diode junctions that are serially connected,each diode junction having an operating curve that is different from apredetermined standard operating curve; said diode junctions beingpre-selected to have a summation of their respective departures fromsaid predetermined standard operating curve substantially zero wherebysaid diode junction temperature sensor has a predetermined voltage dropat a predetermined temperature and a predetermined constant current flowtherethrough and has a substantially linearly varying voltage drop atsaid predetermined constant current within the range of -50* F. to +250*F. for the requisite economy, linearity and interchangeability; b. powersupply means and regulator means for maintaining a substantiallyconstant current flowing through said diode junction temperature sensor;said power supply means and said regulator means being seriallyconnected with said diode junction temperature sensor in the forwardbiased direction; said diode junction temperature sensor being seriallyconnected to electrical common; and c. a readout lead connected with thejuncture of said diode junction temperature sensor and said regulatormeans such that voltage is measured with respect to said electricalcommon to form a signal that is a function of the sensed temperature;said voltage being sensed with no substantial current flow on thereadout lead so as to be insensitive to the length of said readout lead;said readout lead being adapted to be connected into readout means formonitoring the sensed temperature such that any temperature sensor insaid system may be replaced without recalibration and withoutintroducing significant error into the system.
 2. The system of claim 1wherein said regulator means and said diode junction temperature sensorare incorporated into a single temperature measuring device having afirst lead that is connected with said power supply means, a second leadthat is connected with said electrical common and said readout lead isconnected with a readout means for monitoring the sensed temperature. 3.The system of claim 1 wherein said system includes multiplexingapparatus that is connected with a plurality of said readout leads ofsaid respective diode junction temperature sensors, wherein each saidregulator means and diode junction temperature sensor pass asubstantially constant current that is sufficiently low such that is maybe passed continuously without appreciable power consumption and withoutheating said diode junction temperature sensor, and the constant currentfrom said power supply means and said regulator means is continuouslypassed through said diode junction means whereby said multiplexingapparatus may scan rapidly through the readout leads of said diodejunction temperature sensors for monitoring temperatures at a pluralityof widely scattered locations without appreciable instrument lag timebeing elapsed between respective monitorings.
 4. The system of claim 1wherein said constant current is less than 1 millampere.
 5. The systemof claim 1 wherein said constant current is about 100 microamperes.